Fix JS for statistics repartition select form (#2896)
Fix JS for statistics repartition select form (#2896)

* Fix JS for statistics repartition select form

Error was: `s.form is null in extra.js:166:7`
At the same time, disable the form and clears the value while waiting
for the next page to load, to better understand what is happening.

* Whitespace
aledeg/FreshRSS,FreshRSS/FreshRSS,FreshRSS/FreshRSS,romibi/FreshRSS,Alkarex/FreshRSS,marienfressinaud/FreshRSS,FreshRSS/FreshRSS,aledeg/FreshRSS,romibi/FreshRSS,romibi/FreshRSS,Alkarex/FreshRSS,marienfressinaud/FreshRSS,Alkarex/FreshRSS,Alkarex/FreshRSS,FreshRSS/FreshRSS,aledeg/FreshRSS,marienfressinaud/FreshRSS,romibi/FreshRSS,aledeg/FreshRSS,marienfressinaud/FreshRSS